In the 3GPP specification, the radio link control (RLC) protocol layer is responsible for the delivery of protocol data units (PDUs) over the radio interface. A protocol data unit is a unit portion of a data packet that is transmitted over the radio. An acknowledge mode may be used to ensure reliable delivery of the PDU. In this mode, the receiver sends a status report indicating the successful reception of the PDU. It is known to include a polling bit in the RLC PDU header or send a poll control PDU to trigger a status report from the receiver.
In some wireless communication protocols, it is possible for the RLC layer to re-segment a PDU if it has not been received successfully from the initial transmission. The re-segmentation is accomplished by dividing up the original PDU segment into a plurality of PDU segments and then retransmitting each PDU segment individually. The original PDU may have a variable length and each re-segmented PDU segments may be of varying lengths, i.e. different from the length of the other PDU segment. Each of the PDU segments can be either identified by a sub-sequence number or by the first byte location of the segment that corresponds to the original PDU.
Thus, when the receiver needs to indicate the successful reception or loss of a PDU segment, it is possible to do this in one of two ways: by including in each PDU segment the first and last byte locations as they correspond to the original un-segmented PDU or by identifying the PDU segment by including the first byte location and the length of the PDU segment. In order to assist the receiver with reassembling the re-segmented PDU, the last segment of the PDU typically includes a “last segment flag”, LSF.
One consequence of the re-segmentation and the variable length segments, is that when the last segment of the data PDU is lost during transmission, the receiver cannot determine the last byte of the segment or the length of the segment in order to report back to the sender which data unit segment to be re-transmitted. This is particularly true since original PDU does not include the last length indicator and the overall length of the original PDU segment is not known to the receiver. Therefore, when the receiver determines that the last segment field (LSF) has not been received, the receiving device knows that the data is incomplete but cannot accurately relay to the transmitter which portions are missing. Thus it would be beneficial to identify an efficient mechanism to report the identity of the missing data of the re-segmented PDU.
The various aspects, features and advantages of the disclosure will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Detailed Description thereof with accompanying drawings described below. The drawings may have been simplified for clarity and are not necessarily drawn to scale.